Changing back to default language not working

Hello so i have 3 language in my website: English, Chinese, and indonesian(This one is subdomain)

So in my website when i change my website language to chinese it will become like this
‘www.example.com/zh/’
and this is correct right.
But when i tried to change it back to english it will become like this
‘www.example.com/zh//’

so i have to delete it manually from url to change it back to english, how do i fix this? thanks

If you change to chinese and then click chinese menu again …. the link will become like this ‘www.example.com/zh/zh’

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